Integrating Ring‐Size Adjustable Cycloalkyl and Benzhydryl Groups as the Steric Protection in Bis(arylimino)trihydroquinoline‐Cobalt Catalysts for Ethylene Polymerization

Abstract

AbstractCombined condensation and complexation of 2‐acetyl‐5,6,7‐trihydroquinolin‐8‐one, cobalt(II) chloride and the corresponding aniline has been employed as an effective one‐pot route to the 2‐(1‐(arylimino)ethyl)‐8‐arylimino‐5,6,7‐trihydroquinoline‐cobalt(II) chlorides (aryl=2‐Me‐4‐(CHPh2)‐6‐(C5H9)C6H2 Co1, 2‐Me‐4‐(C5H9)‐6‐(CHPh2)C6H2 Co2, 2‐(C5H9)‐4‐Me‐6‐(CHPh2)C6H2 Co3, 2‐(C5H9)‐4,6‐(CHPh2)2C6H2 Co4, 2‐(C6H11)‐4,6‐(CHPh2)2C6H2 Co5, 2‐(C8H15)‐4,6‐(CHPh2)2C6H2 Co6, 2‐F‐4,6‐(CHPh2)2C6H2 Co7, 2‐Cl‐4,6‐(CHPh2)2C6H2 Co8, 2‐Me‐4,6‐(CHPh2)2C6H2 Co9). All complexes have been well characterized including by single crystal X‐ray diffraction for Co3. On activation with either MAO or MMAO, Co1 was the most active for ethylene polymerization with the MAO‐activated precatalyst reaching a peak level at 60 °C (up to 13.66×106 g (PE) mol−1(Co) h−1). By varying the electronic and steric properties of the ortho‐ and/or the para‐substituents of the N‐aryl groups, excellent control over molecular weight could be achieved with values falling in the range 0.97–101.63 kg mol−1 obtainable. Notably, with a benzhydryl group positioned on the ortho‐position of the N‐aryl group, a significant enhancement of the molecular weight was observed, while the least bulky ortho‐cyclopentyl substituent led to increased catalytic activity. As a final point, distinctive microstructural characteristics of the polyethylenes were observed with Co1/MAO producing near quantitative levels of vinyl end groups.